M-16s had all sorts of jamming problems during the Vietnam war. It was so bad that that US soldiers would often pick up & use AK-47s since they were more reliable.
30+ years later, I see the M-16 is still a jamming piece of shit.
http://story.news.yahoo.com/news?tmp.../lynch_book_18
"..Lynch dismisses early reports that she had engaged in a firefight with the Iraqis who ambushed the convoy. Like many soldiers in her company, the M-16 rifle she carried had jammed with grime and airborne sand. She fired no shots, she said.."
P.S.
US special forces are using captured AKs too.